This invention relates to switching power converter circuits and methods and, in particular, relates to a integrated magnetic converter circuit and method with improved filtering.
Switching power converters are used in a wide variety of applications to convert power from one form to another form. For example, dc/dc converters are used to convert dc power provided at one voltage level to dc power at another voltage level. Such dc/dc converters often use rectifier circuits, such as the well-known current-doubler rectifier (CDR) circuit. The CDR circuit has recently been rediscovered for use in high frequency dc/dc converter applications. The low current stresses in the transformer secondary, the inductors, and the rectifiers makes the circuit attractive for dc/dc converters with high output currents. The circuit can be used with different double-ended primary topologies, such as push-pull, half bridge and full bridge.
Early CDR circuits used three separate magnetic components, namely, one transformer and two inductors. However, this configuration results in interconnection losses which negatively impact efficiency, especially in high current applications. Additionally, this configuration results in increased size and cost. To address these problems, integrated magnetic implementations have been proposed that combine the transformer and the inductors into a single magnetic structure with one magnetic core, thereby reducing the size and the interconnection losses.
While this solution addresses some problems, further improvements are still needed. In particular, the effective filtering inductance of existing integrated magnetic implementations for CDR circuits is low due to the use of a single turn secondary for low conduction losses, resulting in high ripple currents and output ripple voltage. The circuit is also more likely to operate in a discontinuous conduction mode when the inductance is low, which is less efficient compared to a continuous conduction mode of operation. Accordingly, an improved rectifier circuit which overcomes one or more of the above problems would be highly advantageous.
According to a first preferred aspect, a converter and rectifier circuit comprises a magnetic core, a first secondary winding, a second secondary winding, a third secondary winding, a first rectifier, a second rectifier and an output capacitor. The first, second and third secondary windings are wound around the magnetic core and are connected to each other. The first rectifier is connected to the first secondary winding and the second rectifier is connected to the second secondary winding. The output capacitor is connected to the first and second rectifiers and is connected in series with the third secondary winding.
According to a second preferred aspect, a dc/dc conversion method comprises providing a voltage to a primary winding of a transformer. The voltage causes a first current to flow in a first secondary winding, a second current to flow in a second secondary winding, and a third current to flow in a third secondary winding, the third current being a summation of the first and second currents. The method further comprises rectifying the first current using a first rectifier, rectifying the second current using a second rectifier, and filtering the third current using inductance of the third secondary winding. The third winding is connected in series with an output capacitor. The method further comprises charging the output capacitor using the third current and providing dc power to a power-consuming device using the output capacitor.